An antenna device such as a parabolic antenna is widely used for, for example, a mobile backhaul known as an RAN (Radio Access Network) which connects a wireless base station with a trunk network. Particularly, in the mobile backhaul, an antenna device of a single beam scheme which radiates a beam in one direction using a reflector and one primary radiator is widely used.
An offset parabolic antenna configured to reduce probability of reception of unnecessary radio waves only using a portion of the reflector of the parabolic antenna is often used as such an antenna device of a single beam scheme.
For example, technology of an offset parabolic reflector adapted not to receive unnecessary radio waves by reducing an aperture plane of a reflector is disclosed in Patent Document 1 as related technology for an antenna device including a reflector antenna of a single beam scheme. According to this technology, in the offset parabolic reflector formed in a shape in which a portion of a rotational parabolic reflector is cut, the reflector is formed so that a shape when a peripheral portion is viewed from a focus position of the offset parabolic reflector is substantially circular. In other words, while spillover (leakage) in a long axis direction increases in an elliptical reflector, it is possible to suppress the spillover to be low and achieve uniformity of an irradiation level in the peripheral portion of the reflector by causing the shape when the peripheral portion is viewed from the focus position of the reflector to be circular. As a result, it is possible to improve irradiation efficiency of the reflector.
Further, for example, technology for a method of realizing a low side lobe characteristic of an offset elliptical beam antenna has been reported in Non-Patent Document 1 as related technology of the offset parabolic reflector.
Further, for example, technology for causing a shape of a contour of a reflector to be a shape along a contour line corresponding to an aperture plane phase deviation caused by a mirror surface aberration in an antenna of a multi-beam scheme which radiates a beam in a plurality of directions from one antenna is disclosed as another related technology in Patent Document 2. According to this technology, it is possible to suppress deterioration of a beam directional characteristic, increase of a side lobe (leaked electromagnetic waves), and reduction of an antenna gain caused by a mirror surface aberration (i.e., a path difference of radio waves due to a difference in reflection position in a mirror surface) by forming the contour of the reflector along the contour line obtained by the mirror surface aberration.